Crank shaft



Patented Dec. 17, 1940 PATENT oFFicE cRANxsnArr Hellmuth Hirth,Stuttgart, Germany, assignor to Birth-Motoren G. m. b. H.,Stuttgart-Zuffenhausen, Germany Application November 26, 1937, SerialNo. 176,612

` In Germany November 30, 1936 1 Claim.

My invention relates to crankshafts. It is an object of the invention toprovide crankshafts, which are lighter Ain weight and stronger and canbe manufactured in a more economical manner than other crankshaftshitherto designed.

As a rule crankshafts are made from forged blanks, and in the case ofquantity production, from swaged blanks. Machining is effected by meansof cutting tools. A great deal of power and time is spent on the cuttingdown of a considerable part of the valuable material to value- Y lesscuttings. The shape given to the individual parts of the shaft islfrequently determined more by considerations of machining rather than byconsiderations of the most favorable stressing in operation, and theparts are besides made too heavy, which likewise amounts to a waste ofmaterial. Crankshafts are exposed mainly to bend-v ing and torsionalforces, and it is a well known 2o fact that the outermost fibres of thematerial contribute mostly to the transmission of these forces,'the bresin the interior of the shaft being far less ellicaceous andbeingtherefore utilized only partly. This is the reason why parts 25 ofshafts are mostly made hollow, for instance by boring, which once moreamounts to a wasting of valuable material.

I avoid this waste and utilize the material best suited for this purposein thel most economical 3o manner, at the same time keeping the weightof the crankshaft particularly low by forming the shaft and moreespecially the cranks as hollow bodies, the walls of which consist ofpieces of material of substantially the thickness corresponding 35 tothe wall thickness of the finished hollow body. I prefer making theshafts and more especially the cranks from sheet metal pressed intoshape to form hollow shells of the shape required. With equal weight andmaterial sheetmetal always 40 possesses a higher mechanical strengththan a body of higher wall thickness, and this in view of the particularmanner in which it has been produced, since the rolling process leads toa more intense kneading and to a greater compression 45 of the material.Defects in the material can be traced and avoided or excluded morereadily.

Manufacture of the parts of the shaft from sheet metal is effectedWithout cutting and therefore without any loss of material by merepress- 5o ing and drawing. The single parts of the sheet metal shaft arepreferably connected with each other by welding, and the hollow shaftsthus obtained are then treated further in the same manner as solidforged blanks. 55 'I'he modern welding processes render it possible toeffect all such connections quickly and in an absolutely safe manner.Welding seams, if carefully produced, possess a mechanical strengthrunning up to 60 lig/mm2. However, since thesel seams are notparticularly fit for trans mitting torsional or rotatory forces, I mayprovide' special means for transmitting such forces, whereby thewelding'seams are relieved.

In the drawing amxed to this specification and forming part thereofcrankshafts embodying my 10 inventionvare illustrated diagrammaticallyhy way of example.

In the drawing,

Fig. 1 is an axial section, and

Fig. 2 a cross section on the line A-B in Fig. 1, 15 of the firstmodication.

Fig. 3 is an axial section, partly in elevation, of a secondmodification.

Figs. 4 and 5 are axial sections of a crank pin and a crank, and of abearing journal. respectively.

l Referring to the drawing and rst to Figs. 1 and 2, the shaft proper land the crank pins 2 may be formed from` sheet metal strips by rolling,the longitudinal seam being closed by welding. AlternativelyI may usedrawn steel tubes in the manufacture of these parts. In order to obtaina favorable transmission of the rotatory forces, I form the welding endsof the cylindrical pins with embossed portions 3 which project intocorresponding depressions of the cranks and serve to carry them along.Preferably these embossed portions may have the form of corrugations. Ithereby at the same time obtain a considerable lengthening of theWelding seam and a larger surface for the connecting of the parts.

Each crank is here composed of two halves 4 formed with perforationsinto which project the pins I and 2. The edges of the perforations are lbeaded to form annular anges and are corrugated in such manner that thepins fit tightly into them.

When assembling a shaft such as here shown, the corrugated end of thepin or shaft I is rst introduced into one of the hollow cranks 4 and isconnected with it by welding at the places at 5 and 6. In a similarmanner the crank pin 2 is fixed in the other crank. Now the two halvesthus prepared are assembled and welded together at l. Finally the endsof the pins or shaft are connected by welding with the other half of thecranks at 8 and 9,'respectively.

In this manner the crankshaft as a whole is produced, to be thenannealed in order to remove all internal stresses, whereupon it ismachined in the usual manner.

This manner of producing crankshafts can also be applied to theproduction of crankshafts which can be taken apart and reassembled, suchas the crankshaft with toothed ends invented by the applicant.

Fig. 3 illustrates a shaft of this latter kind constructed in accordancewith the present invention. The cranks are designed exactly as describedwith reference to Figs. 1 and 2. The bearing pins I and Il form separatepieces, being connected with the cranks by means ofltheir toothed ends,I being the part of the shaft transmitting the driving force to the airpropeller or the like. The pins Iliand I2, being toothed at both ends,form the bearing pins for the main and connecting rod bearings of theshaft. hardened condition they may serve as sliding bearingsorpreferably as rolling bearings. pins Il, I2 are connected-with thecranks by means of bolts I3, which also form tubular bodies formed atboth ends with screw thread of different pitch, so that only thedifference of pitch becomes effective. Interiorly these bolts are formedwith means, known as such, for introducing a socket wrench, being, forinstance, formed with a slot, a square or hexagonal perforation or thelike, indicated at I4, or with teeth, by means of which the pin can befixed in place by screwing.

The different pitch of the screw threads enables the parts of the shaftto be compressed very firmly. Apart from that this connection is knownto not require any separate lofking means.

Since the toothed ends of the parts of the shaft must possess a certainwidth in order to be able to transmit forces and since pieces made ofsheet metal lack such width, the inserts such as I0 are preferably madeof considerably stronger material, for instance of thick-walled steeltube or of a solid rod.. These parts are also formed with a corrugatedsurface, the corrugations being formed by drawing and not requiring anymachining. In the case of smaller and lighter Inl The

shafts the corrugations 3 need only be provided on the toothed end ofthe inserts I0, the other end being made smaller in diameter and with asmooth outer surface, as shown in Fig. 4. 'This construction enables meto weld the connections also in the case where the pins are spaced onlya small distance from each otherI i. e. with cranks of small radius.

As shown in Fig. 5, the inserts I0 may also be conical. In that case theaperture left in the inserts must at least allow the socket Wrench to beintroduced for the fixing of the connecting bolts I3.

Instead of welding also any other mode of connection of the parts may beused, for instance by beading their edges together either all around or,in the case of a connection by tenons and mortisesor by dovetailing, byinserting the projecting parts.

Instead of sheet metal, as this term is commonly understood, I may alsouse pieces of some other kind which possess a predetermined wallthickness which corresponds to the Wall thickness of the parts of thecrankshafts to be produced therefrom, for instance cup-shaped or otherhollowbodies produced in some manner other than by casting.

I Wish it to be understood thatI do not desire to be limited to theexact details ofv construction shown and described for obviousmodifications will occur to a person skilled in the art.

I claim:

A crankshaft comprising in combination, a plurality of cranks formedwith openings, a tubular member extending between and connectingadjacent cranks, corrugated crank wall portions surrounding saidopenings, corrugated end portions provided on said tubular member andinserted in said openings so as to interlock with said corrugated crankWall portions, and welding seams firmly uniting said interlockinglportions -into integral structural parts, said corrugations serving to.extend the length of said welding seams.

' HELLMUTH HIRTH.

